The human inner clock regulates far more than just being tired in the evening and waking up hopefully on time in the morning - if it is disturbed, stress, jet lag or serious long-term psychological damage are the result. Nevertheless, euphoric chronobiologists should not intervene too hastily in the body's stuttering daily clock.
A tiny bit of triumph shimmers between the lines of Daniel Forger: "I've known that for a year or two. People generally said 'ridiculous'; and 'what do you know about it'." The researcher from the University of Michigan believes that this should now be over: sometimes theoreticians can also show biologists what a rake is.
Forger is a mathematician and has been investigating biological issues with his own resources for a long time - such as the principle of the internal clock. In order to understand them better, he had some time ago begun to theoretically model circadian rhythms in living things and had encountered a strange thing: Either his models were wrong - or the prevailing theory of biochemists on the mechanisms that determine the internal clock of living things makes it tick. At the center of the deviation: the already famous clock protein "Period".
The protein is at the center of the control circuit made up of numerous protein adjusting screws that interact with each other and alternately determine the daily events in the cell depending on the time of day. In mammals, for example, the transcription factors "Clock" and "Bmal1" tinker together in the cell nucleus and cause, among other things, the construction of period. This accumulates in the cytoplasm and then, when a certain threshold concentration is exceeded, in turn inhibits the clock Bmal1 protein responsible for its existence. The constantly working breakdown proteins then reduce the period concentration back to the initial level.
In any case, the amount of period in the cells determines – that much was clear – the internal time of a cell. And if something goes wrong when leveling out the period, this does not remain without consequences for the day-night rhythm of the organism, as was recognized in the example of the golden hamster in 1988: In Mesocricetus auratus, the so-called tau mutation shortens the circadian rhythm two to four hours. In humans, a similar genetic defect causes the "familial advanced sleep phase syndrome" (familial advanced sleep phase syndrome, FASPS) – those affected get up very early and already feel heavy on bed in the late afternoon.
In both cases, the cause is a point mutation in the casein kinase I enzymes (CKIe or CKId) that are jointly responsible for period degradation. The hamster mutation demonstrably slows down CKIe - in the test tube experiment - and thus perhaps - in reality - slows down the disappearance of periods a little bit. Period then accumulates faster, exceeds the threshold concentration sooner and inhibits the clock Bmal1 replenishment apparatus earlier. This makes the clock tick faster: hamsters with only one mutated gene have a 22-hour cycle, while animals with tau mutations on both chromosomes have a cycle of only 20 hours.
So much for the common theory. It must be wrong, says Forger - because in his mathematical model the mutation of CKIe should lead to the period disappearing more quickly, but not being broken down more slowly, in order to explain the observed shortening of the day/night period in those affected. This could work if the mutation does not prevent CKIe from activating degradation proteins, but actually accelerates this activation due to the mutation. The faster degradation would then also lead to the Period-mediated inhibition of Clock-Bmal1 being quickly lifted again - and Period being delivered again just as quickly.
So whether – as the hypothesis valid up to now predicts – Clock-Bmal1 is quickly inhibited, or – according to Forger's model – this inhibition is lifted all the more quickly: both can in principle make the physiological day shorter than usual. That's exactly what the mathematician said for a long time to everyone who didn't want to hear it. Now, together with the University of Utah physician David Virshup, he tested in living hamster cells what really happens with CKIe: inhibition or hyperactivity.
The result proved Virshup and Forger right: Tau-mutated CKIe enzymes degraded period proteins up to 57 percent faster than unmutated ones - apparently due to an increased influence of the cellular wrecking ball, the proteasome. CKIetau probably ensures that Period is marked as waste by phosphate markers in those cell regions in which the cell's own waste disposal is active. This apparently applies to all of the currently known tau mutations - not only in hamsters, but also in human cells or those of the fruit fly, the scientists determined.
The question remains how this connection could have escaped chronobiologists so far. After all, they had demonstrated tau-induced inhibition of CKI in the test tube, hadn't they? But in vitro is not in vivo, explains Forger: This can have a particular impact if other players in the test tube do not function as they do under natural conditions. Such underestimated participants could be the opponents of kinases such as CKI, the phosphatases - clockwork is very complicated. And it is better not to interfere with such a clockwork until it is clear in which direction the hands of the clock are actually running.